Multilayered Particles Research Articles

Exfoliated Ferrierite-Related Unilamellar Nanosheets in Solution and Their Use for Preparation of Mixed Zeolite Hierarchical Structures.

Direct exfoliation of layered zeolites into solutions of monolayers has remained unresolved since the 1990s. Recently, zeolite MCM-56 with the MWW topology (layers denoted mww) has been exfoliated directly in high yield by soft-chemical treatment with tetrabutylammonium hydroxide (TBAOH). This has enabled preparation of zeolite-based hierarchical materials and intimate composites with other active species that are unimaginable via the conventional solid-state routes. The extension to other frameworks, which provides broader benefits, diversified activity, and functionality, is not routine and requires finding suitable synthesis formulations, viz. compositions and conditions, of the layered zeolites themselves. This article reports exfoliation and characterization of layers with ferrierite-related structure, denoted bifer, having rectangular lattice constants like those of the FER and CDO zeolites, and thickness of approximately 2 nm, which is twice that of the so-called fer layer. Several techniques were combined to prove the exfoliation, supported by simulations: AFM; in-plane, in situ, and powder X-ray diffraction; TEM; and SAED. The results confirmed (i) the structure and crystallinity of the layers without unequivocal differentiation between the FER and CDO topologies and (ii) uniform thickness in solution (monodispersity), ruling out significant multilayered particles and other impurities. The bifer layers are zeolitic with Brønsted acid sites, demonstrated catalytic activity in the alkylation of mesitylene with benzyl alcohol, and intralayer pores visible in TEM. The practical benefits are demonstrated by the preparation of unprecedented intimately mixed zeolite composites with the mww, with activity greater than the sum of the components despite high content of inert silica as pillars.

Internal morphology-dependent resonances of a coated spherical particle

Morphology-dependent resonances (MDRs) for a coated spherical particle are important because of their extensive applications. However, MDRs for coated spherical particles are more complicated than those for homogeneous particles. In this paper, a general expression is proposed for calculating the scattering efficiency of a specific layer of coated particle. Reformulations of internal scattering efficiency are made, which provides a new, to the best of our knowledge, method to investigate the resonance in the core and in the shell independently. MDRs in the core can be shown in four cases on the outmost scattering efficiency curve. To investigate the reason of the resonance, the relationships between MDRs in the core, outmost scattering efficiency, and partial wave are analyzed. It is numerically shown that the expressions are reliable and efficient, which provides a theoretical fundamental for studying of resonances of multilayered particles and for measurement.

Ti-doping of hematite films with multilayered particle size distribution by magnetron sputtering

α-Fe2O3 films with a layered distribution of nano and submicron particles were synthesized and Ti-doped successfully. Morphology, element and phase composition, electrochemical properties of one-layered, multilayered, and Ti-doped films were investigated. Doped multilayered hematite films have higher catalytic water oxidation efficiency than both undoped films.

Adsorption-Reaction Processes Between Gelatin and PDMS-E Emulsion Droplets.

In this work, the effects of droplet size and reaction time on the adsorption-reaction processes between gelatin and α-[3-(2,3-epoxypropoxy) propyl]-ω-butyl-polydimethylsiloxane (PDMS-E) emulsion droplets were studied. Gelatin molecules were only physically adsorbed on the surface of the PDMS-E droplet in the 0–75 min range, which was unrelated to the droplet size (100–1000 nm). For the small-size droplets (<410 nm), the physical adsorption proceeded over 75 min followed by agglomeration. For middle-size droplets (410–680 nm), the physical adsorption finished at 125 min; subsequently, the nucleophilic reaction between the primary amino group and the epoxy group began to happen, and globular-like or core–shell colloidal particles were formed. For large-size droplets (>680 nm), the nucleophilic reaction occurred at 75 min and produced core–shell or multi-layered colloidal particles. In a word, the physical absorption or nucleophilic reaction between gelatin and PDMS-E emulsion droplets could be controlled by controlling the droplet size and reaction time. Furthermore, the soft tissue paper coated with large-size droplets exhibited excellent resistance to water permeability and flame-resistant performance, which were carried out by water resistance and flammability tests.

A new surface tension formulation in smoothed particle hydrodynamics for free-surface flows

When the surface tension force acts on the multi-layer particles near the free surface, the integral of the previous surface delta function through the free surface is less than 1 because of the boundary truncation and kernel truncation, which leads to the problem that the numerical results cannot converge to the theoretical solution. Although a few studies have recognized this problem, it has not been completely solved. In the present work, a new formulation of the continuum surface force (CSF) model in smoothed particle hydrodynamics (SPH) is developed for free-surface flows, in which two measures are taken to correct the shortcomings of the commonly used formulations. In the first measure, a new surface delta function that meets the normalization requirement is proposed to solve the problem that the integral of the previous surface delta function through the free surface is less than 1 when the surface tension force acts on the multi-layer particles near the free surface. This normalization measure is key to make the numerical results with surface tension converge to the theoretical solution. In the second measure, the normal vector and curvature of the free surface are derived by the finite particle method (FPM) to improve their calculation accuracy. Through the one-dimensional tests, the new surface delta function is analyzed and compared with existing formulations. Through the two-dimensional tests on a unit circle, the new normal vector and curvature of the particles near the free surface are implemented and also compared with previous formulations. Finally, the proposed formulation is validated using eight two-dimensional and three-dimensional numerical cases with surface tension. The results show that the proposed formulation solves the problem that the numerical results of the previous formulation cannot converge to the theoretical solution, and it is accurate and robust in calculating the free-surface flows with surface tension.

Electrocatalytic Hydrogen Evolution Reaction with Multilayer Graphene-Covered Ni Particles Synthesized by Microwave-Assisted Catalytic Methane Decomposition

It is known that the type of electrocatalysts used in the hydrogen evolution reaction (HER) are critical for energy technologies such as water splitting and hydrogen fuel cells. Thus, in recent years, increasing attention has been paid to the development of noble metal-free electrocatalysts. It has recently been reported that Ni–C-based catalysts exhibit HER activity comparable to that of Pt in an acidic medium. Moreover, we have recently developed a new metal–carbon powder, which contained multilayer graphene-covered Ni particles as the main component, synthesized by multimode microwave-assisted catalytic CH4 decomposition using a multimode microwave reactor. Thus, in this study, we investigated the electrocatalytic HER over the Ni–C powder using a digital potentiostat equipped with a potential sweep unit. Figure 1 shows the current–potential curve in the presence or absence of dissolved oxygen in an aqueous H2SO4 solution; the curve was obtained using a carbon paste electrode filled with the Ni–C powder. A reduction current based on HER was observed from approximately 0.0 V (referred vs. SHE), while the onset potential was shown to be slightly affected by the presence or absence of dissolved oxygen. Therefore, the Ni–C powder can be used as a noble metal-free electrocatalyst to implement the HER with excellent electrochemical performance in acidic medium. *Figure 1. Linear sweep voltammograms with the carbon paste electrode (Φ = 3 mm) filled with the Ni–C powder, synthesized by a multimode microwave-assisted process in an acidic solution under different atmospheres. SR = 10 mV/s. Figure 1

In-situ SEM compression of accordion-like multilayer MXenes

A relatively new and large class of materials, two-dimensional (2D) early transition metal carbides (MXenes), produced by etching of A elements from their parent MAX phases, have demonstrated outstanding performance in many applications. However, the mechanical behavior of MXenes, which is critical for device fabrication and performance, has not been sufficiently investigated. In this work we report the results from in-situ scanning electron microscopy (SEM) uniaxial compression experiments conducted on two types of multilayer accordion-like MXene particles, Ti2CTx and Ti3C2Tx, along both in-plane and out-of-plane directions. Significant anisotropic behavior was observed associated with progressive failure mechanisms. Molecular dynamics (MD) modeling was conducted to analyze the behavior of intact and defected monolayer Ti2C and Ti3C2 MXenes in tension and compression. Structural analysis for both in- and out-of-plane uniaxial compression is presented and compared with experimental data, revealing that the overall mechanism is controlled by the intrinsic elastic and plastic properties of MXenes, as well as their multilayer structures. The intrinsic material properties were estimated based on structural analysis from experimental results.

AC Electrokinetics of Salt-Free Multilayered Polymer-Grafted Particles.

Interest in the electrical properties of the interface between soft (or polymer-grafted) nanoparticles and solutions is considerable. Of particular significance is the case of polyelectrolyte-coated particles, mainly taking into account that the layer-by-layer procedure allows the control of the thickness and permeability of the layer, and the overall charge of the coated particle. Like in simpler systems, electrokinetic determinations in AC fields (including dielectric dispersion in the 1 kHz–1 MHz frequency range and dynamic electrophoresis by electroacoustic methods in the 1–18 MHz range) provide a large amount of information about the physics of the interface. Different models have dealt with the electrokinetics of particles coated by a single polymer layer, but studies regarding multi-layered particles are far scarcer. This is even more significant in the case of so-called salt-free systems; ideally, the only charges existing in this case consist of the charge in the layer(s) and the core particle itself, and their corresponding countercharges, with no other ions added. The aims of this paper are as follows: (i) the elaboration of a model for the evaluation of the electrokinetics of multi-grafted polymer particles in the presence of alternating electric fields, in dispersion media where no salts are added; (ii) to carry out an experimental evaluation of the frequency dependence of the dynamic (or AC) electrophoretic mobility and the dielectric permittivity of suspensions of polystyrene latex spherical particles coated with successive layers of cationic, anionic, and neutral polymers; and (iii) finally, to perform a comparison between predictions and experimental results, so that it can be demonstrated that the electrokinetic analysis is a useful tool for the in situ characterization of multilayered particles.

Fabrication and evaluation of electroplated diamond grinding rods strengthened with Cr-C deposit

Cr-C-Ni-diamond composite deposits with synthetic diamond particles of 50 μm in average size were electroplated onto a medium-carbon steel rod to fabricate electroplated diamond grinding rods. To make an electroplated Cr-C-Ni-diamond grinding rod with a high diamond density, three sequential electroplating processes were proposed, including Ni undercoating, Ni-diamond co-electroplating, and Cr-C strengthen-electroplating. The Cr-C strengthening deposit was prepared in an eco-friendly Cr3+-based plating bath. A composite Cr-C-Ni-diamond deposit with multi-layered diamond particles could be prepared on the steel rod substrate by repeating the proposed three sequential electroplating processes. After electroplating, some of the prepared grinding rods were annealed at 500 °C for 30 min to increase the hardness of Cr-C deposit. As-plated and annealed electroplated Cr-C-Ni-diamond grinding rods with one- and two-layered diamond particles were used to grind slots in Al2O3 plates in a depth of 5 mm to evaluate their grinding-life performances. Based on the results of grinding tests, the ground length of an electroplated Cr-C-Ni-diamond grinding rod was significantly increased after annealing at 500 °C for 30 min, and the length was further extended by electroplating two layers of Cr-Cs-Ni-diamond composite deposit. A relatively long ground length of 1320 mm was achieved from the 500 °C-annealed electroplated diamond grinding rod with two-layered diamonds, but only 30 mm from the as-plated one. It was evidenced that an anneal-hardened Cr-C deposit can serve as a competent strengthening layer in the electroplated diamond tool.

Electrocatalytic Hydrogen Evolution Reaction with Multilayer Graphene-Covered Ni Particles Synthesized by Microwave-Assisted Catalytic Methane Decomposition

We developed a new method for the production of large amounts of carbon–nickel (C–Ni) powder, which contained multilayer graphene-covered Ni particles as the main component, using multimode microwave-assisted catalytic CH4 decomposition. Electrocatalytic hydrogen evolution reaction of the C–Ni powder in acidic solution was investigated using electrochemical method. The C–Ni powder can be used as a noble metal-free electrocatalyst to implement the hydrogen evolution reaction with good electrochemical performance in the acidic solution.

Composites Based on Nanodispersed Nickel, Graphene-Like Carbon, and Aerosil for Catalytic Hydrogenation of Furfural and Quinoline

It is shown that a composite containing nickel nanoparticles and carboneous multi-layer graphene-like particles on aerosil, prepared by pyrolysis of deposited nickel complex with melamine, catalyzes hydrogenation of furfural to furfuryl alcohol as well as hydrogenation of quinoline to 1,2,3,4-tetrahydroquinoline. The highest yield of hydrogenation products (27% of furfuryl alcohol at 100°C, 30 atm H2, and 25% of quinoline at 100°C, 100 atm H2) is achieved with the use of composites with higher nickel content (8.4%) and higher size of defect-free graphene areas (ratio of band intensities ID/IG in Raman spectrum 0.9).

Role of surface coverage of alumina with Pt nanoparticles deposited by laser electrodispersion in catalytic CO oxidation

This work elucidates the role of surface coverage of alumina with Pt nanoparticles on the catalyst efficiency in CO oxidation. Size-selected Pt nanoparticles were deposited on the outer surface of alumina pellets by the laser electrodispersion technique. The alumina surface coverage with Pt varied from 0.04 to 3.5 nanoparticle layers and affected the Pt electronic state and catalyst efficiency. Even in the multilayer coatings nanoplatinum particles remained isolated. The catalysts were tested in CO oxidation at CO/O2 ratios of 0.2, 1 and 2 in the temperature-programmed and pulse reaction modes. At CO/O2 = 0.2 the temperature of 50% CO conversion increased with decreasing the surface coverage with Pt particles. At CO/O2 = 2 the decrease in the surface coverage enhanced the catalyst activity. Pt0 dominates only in multilayer catalysts, however, approximately half of platinum remained non-oxidized even at such a low metal loading as 0.01 wt%. The change in the electronic state of platinum under the thermal treatment in the reaction mixture affected the catalyst efficiency. The oxidation state of Pt depended on the metal loading, reaction temperature, CO/O2 ratio in the reaction mixture, mode of its feeding and surface coverage with Pt nanoparticles that influenced the interparticle and particle – support interactions.

Effects of dielectric gradients‐mediated ions partitioning on the electrophoresis of composite soft particles: An analytical theory

AbstractIn this work, we report original analytical expressions defining the electrophoretic mobility of composite soft particles comprising an inner core and a surrounding polymer shell with differentiated permeabilities to ions from aqueous background electrolyte and to fluid flow developed under applied DC field conditions. The existence of dielectric permittivity gradients operational at the core/shell and shell/solution interfaces is accounted for within the Debye–Hückel approximation and flat plate configuration valid in the thin double layer regime. The proposed electrophoretic mobility expressions, applicable to weakly to moderately charged particles with size well exceeding the Debye layer thickness, involve the relevant parameters describing the particle core/shell structure and the electrohydrodynamic features of the core and shell particle components. It is shown that the analytical expressions reported so far in literature for the mobility of hard (impermeable) or porous particles correspond to asymptotic limits of the more generic results detailed here. The impacts of dielectric‐mediated effects of ions partitioning between bulk solution and particle body on the electrophoretic response are further discussed. The obtained expressions pave the way for a refined quantitative, analytical interpretation of electrophoretic mobility data collected on soft (nano)particles (e.g., functionalized dendrimers and multilayered polyelectrolytic particles) or biological cells (e.g., viruses) for which the classical hard core‐soft shell representation is not appropriate.

Spatially resolved X-ray absorption spectroscopy investigation of individual cation-intercalated multi-layered Ti3C2Tx MXene particles

Ti3C2Tx MXene is a two dimensional (2D) material possessing highly active hydrophilic surfaces coupled with high metallic conductivity. Cation intercalation between the Ti3C2Tx nanosheets has a significant role in many applications such as water purification, desalination, and electrochemical energy storage. The pseudocapacitive charging mechanism involving surface redox reactions at the Ti3C2Tx surface enables higher energy densities than electrical double-layer capacitors, and higher power densities than batteries. In this context, the oxidation state of surface Ti atoms involved in redox reactions has a high impact on the capacitance of Ti3C2Tx MXene and this can be impacted by cation intercalation. The electronic structure of multi-layered Ti3C2Tx particles can be investigated by X-ray absorption (XA) spectroscopy, while also benefitting from a high spatial resolution of 30 nm from X-ray photoemission electron microscopy. In this work, the XA spectra from multi-layered intercalated Ti3C2Tx particles of different thicknesses were recorded at the Ti L- and O K-edges. The Ti oxidation state in pristine, Li-, and Mg-intercalated Ti3C2Tx was found to be thickness-dependent, while Na- and K-intercalated Ti3C2Tx particles did not reveal differences upon changing thickness. This work demonstrates thickness-dependent modification of the MXene surface chemistry upon cation intercalation in different individual Ti3C2Tx particles.

Mechanical Integrity of Conductive Carbon-Black-Filled Aqueous Polymer Binder in Composite Electrode for Lithium-Ion Battery.

The mechanical stability of aqueous binder and conductive composites (BCC) is the basis of the long-term service of composite electrodes in advanced secondary batteries. To evaluate the stress evolution of BCC in composite electrodes during electrochemical operation, we established an electrochemical–mechanical model for multilayer spherical particles that consists of an active material and a solid-electrolyte-interface (SEI)-enclosed BCC. The lithium-diffusion-induced stress distribution was studied in detail by coupling the influence of SEI and the viscoelasticity of inorganic-filler-doped polymeric bonding material. It was found that tensile hoop stress plays a critical role in determining whether a composite electrode is damaged or not—and circumferential cracks may primarily initiate in BCC, rather than in other electrode components. Further, the peak tensile stress of BCC is at the interface with SEI and does not occur at full lithiation due to the relaxation nature of polymer composite. Moreover, mechanical damage would be greatly misled if neglecting the existence of SEI. Finally, the structure integrity of the binder and conductive system can be effectively improved by (1) increasing the carbon black content as much as possible in the context of meeting cell capacity requirements—it is greater than 27% and 50% for sodium alginate and the mixtures of carboxy styrene butadiene latex and sodium carboxymethyl cellulose, respectively, for composite graphite anode; (2) reducing the elastic modulus of SEI to less than that of BCC; (3) decreasing the lithiation rate.

Dynamic Solid-State Ultrasound Contrast Agent for Monitoring pH Fluctuations In Vivo.

The key challenge for in vivo biosensing is to design biomarker-responsive contrast agents that can be readily detected and monitored by broadly available biomedical imaging modalities. While a range of biosensors have been designed for optical, photoacoustic, and magnetic resonance imaging (MRI) modalities, technical challenges have hindered the development of ultrasound biosensors, even though ultrasound is widely available, portable, safe, and capable of both surface and deep tissue imaging. Typically, contrast-enhanced ultrasound imaging is generated by gas-filled microbubbles. However, they suffer from short imaging times because of the diffusion of the gas into the surrounding media. This demands an alternate approach to generate nanosensors that reveal pH-specific changes in ultrasound contrast in biological environments. Silica cores were coated with pH-responsive poly(methacrylic acid) (PMASH) in a layer-by-layer (LbL) approach and subsequently covered in a porous organosilica shell. Transmission electron microscopy (TEM) and confocal laser scanning microscopy (CLSM) were employed to monitor the successful fabrication of multilayered particles and prove the pH-dependent shrinkage/swelling of the PMASH layer. This demonstrates that reduction in pH below healthy physiological levels resulted in significant increases in ultrasound contrast, in gel phantoms, mouse cadaver tissue, and live mice. The future of such materials could be developed into a platform of biomarker-responsive ultrasound contrast agents for clinical applications.

Hydrophobic and Stable MXene-Polymer Pressure Sensors for Wearable Electronics.

Ti3C2Tx MXene has exhibited great potential for use in wearable devices, especially as pressure sensors, due to its lamellar structure, which changes its resistance as a function of interlayer distance. Despite the good performance of the reported pure MXene pressure sensors, their practical applications are limited by moderate flexibility, excessively high MXene conductivity, and environmental effects. To address the above challenges, we incorporated multilayer MXene particles into hydrophobic poly(vinylidene fluoride) trifluoroethylene (P(VDF-TrFE)) and prepared freestanding, flexible, and stable films via spin-coating. These films were assembled into highly sensitive piezoresistive pressure sensors, which show a fast response time of 16 ms in addition to excellent long-term stability with no obvious responsivity attenuation when the sensor is exposed to air, even after 20 weeks. Moreover, the fabricated sensors could monitor human physiological signals such as knee bending and cheek bulging and could be used for speech recognition. The mapping spatial pressure distribution function was also demonstrated by the designed 10 × 10 integrated pressure sensor array platform.

Controllable fabrication of biodegradable Janus and multi-layered particles with hierarchically porous structure

We introduce a facile strategy to synthesize both Janus and multi-layered microparticles with hierarchically porous structure by adopting a simple oil-in-water emulsion technique. Incorporation of a minute quantity of non volatile poor solvent such as mustard oil into the emulsion comprising of biodegradable polymers such as Poly(lactic-co-glycolic acid)(PLGA) and Poly(l-lactic acid)(PLLA), led to a precisely controlled phase separation. This resulted in the formation of Janus or multi-layered particles with hierarchically porous structure depending on the amount of mustard oil and viscosity/crystallinity of the polymers employed. No additional toxic porogen needs to be added to induce the porosity. The mechanism of formation of various architectures was explored with the supportive evidences primarily from in situ optical microscopy along with interfacial tension measurements. Moreover, we also show the potential application of these unique particles in delivering multiple actives by encapsulating and releasing the dual actives (antibacterial and antioxidant) in controlled fashion for prolonged period of time (60 days). The release profiles of the dual actives were found to be influenced by the porosity as well as architecture of the particles.

Magnetic properties, responsiveness, and stability of paramagnetic dumbbell and ellipsoid colloids

A layer-by-layer method is used to synthesize paramagnetic metal/polymer multi-layered colloidal particles. By taking advantage of recent advances in the synthesis of polymer colloids with various shapes and layer-by-layer assembly, superparamagnetic dumbbell colloids are fabricated with different aspect ratios and asymmetries between lobes. We characterize the surface coverage of magnetic nanoparticles on the anisotropic host particles and the magnetic response of the particles by magnetometry. The synthesized particles are colloidally stable, but in a magnetic field, form persistent microstructures through induced interactions. These column-like microstructures are reversible and readily disperse by Brownian motion. The magnetic nanoparticle concentration during synthesis provides a means to control the magnetic response of the composite nanoparticle. The method is extended to prolate ellipsoid nanoparticles with aspect ratios between 3.4 and 4.2.

Broadband transmission-type 1-bit coding metasurface for electromagnetic beam forming and scanning

Coding metasurfaces make it possible to manipulate electromagnetic (EM) waves digitally by means of several discrete particles. Hence, there have been rapid advances in this field recently. Here we propose a novel design of a broadband transmission-type coding metasurface, which is valid to both x - and y -polarized EM incidences from 8.1-12.5 GHz while satisfies the requirements of 1-bit coding without changing the polarization. Two types of multi-layer coding particles with different geometrical parameters are adopted to represent the digital states “0” and “1”, which are easily promoted to terahertz and optics through modifying the size scale. To verify the ability to manipulate the EM waves, we first adopt the coding metasurface to achieve broadband beam forming by converting spherical waves to plane waves and realize high-directivity pencil beam in far field with low side lobes. We further arrange the particles according to the coding sequence 010101… to steer two symmetrical beams in different directions controlled by frequencies with the maximum range of the scanning angle of 30°-50.5°. The good agreements between the simulated and measured results validate the proposed broadband coding metasurface, indicating its huge potential in communication and radar imaging systems.